This invention pertains to methods of controlling in the steady state, neutron albedo in toroidal fusion devices, and in particular, to methods of controlling the flux and energy distribution of collided neutrons which are incident on an outboard wall of a toroidal fusion device.
A number of approaches are currently being studied in the development of nuclear fusion as a long-term energy source. Several of the more promising approaches involve the confinement by means of strong magnetic fields of a highly energetic plasma possessing extremely high temperatures and densities so as to cause the fusing of atomic nuclei, such as deuterons and tritons, and the resulting production of energy.
It has been found that one of the most efficient configurations for optimum plasma containment is in the form of a toroid or "doughnut". This has given rise to the tokamak fusion reactor design which is currently under intensive study by research groups in a number of countries. By means of a circular arrangement of powerful magnets, the toroidal magnetic field for confining an energetic plasma is formed. In addition to tokamaks, other toroidal plasma devices such as stellerators, levitrons, spherators, floating-ring multipoles and the like toroidal devices, are being considered.
It is important to investigate during the operation of early plasma confinement devices, and in other situations where high energy neutron environments are encountered, the effects of a fusion radiation environment on containment materials, reactor hardware, and associated equipment, such as electronic circuits and electrical control devices. Hence, a principal objective of early fusion plasma devices is to provide a radiation effects facility for conducting nuclear radiation damage and hardening programs in fast neutron environments. Tokamak fusion generators provide a much larger uniformly irradiated test volume, and can give more faithful spectral simulations of thermonuclear environments than accelerator-driven point neutron sources or pulsed fastfission reactors. Further, radiation effects facilities provide a simulated high-energy neutron environment for generalized studies of the effects of that environment on biological, metallurgical and chemical systems. Tokamak test facilities of this type, according to present designs, are long-pulsed sources, producing relatively low neutron dose rates (approximately 10.sup.5 rads/s) that limit application of these facilities to damage programs with devices and subsystems that are sensitive to integrated radiation dose, rather than dose rate. The relatively low neutron dose rates inherent in next-generation tokamak operation must be enhanced at given test regions if the facility is to provide a useful test environment. Toroidal confinement devices will typically provide test locations for radiation test modules lying just outside the more accessible outboard boundary of the plasma containment vessel.
To meet a variety of simulation requirements, radiation effects facilities should provide a control over the neutron energy spectrum distribution, as well as the ratio of gamma flux to neutron flux. Exact simulation of gamma-ray fields is of secondary importance in tokamak-type radiation effects facilities because many other facilities offer gamma fields of much higher intensity. Nonetheless, a substantial gamma field will exist in a tokamak environment, and if neutron damage effects are to be more completely isolated, the gamma fields must be suppressed.
In a controlled thermonuclear reactor, the neutron flux must be relied upon to provide a sufficient level of tritium breeding, tritium being one of the principal fuel components of a D-T fusion reactor. In toroidal reactors, especially with magnetic divertors, tritium breeding blanket modules will not completely cover the plasma containment vessel. It is important that tritium breeding be maximized wherever breeding regions exist, in order to have adequate tritium production, and albedo control is necessary to increase the neutron flux on these breeding modules. Breeding enhancement is especially important in producton reactors where, because of space limitations, only limited areas are available for tritium breeding modules. In smaller reactors where access to the inboard blanket shield region is difficult, the placement of tritium breeding blankets may have to be limited to selected outboard portions of the reactor.
Also, the neutron flux generated in a controlled thermonuclear reactor provides a fast neutron beam output of increased energy and density levels required for general research. As a research tool, it is particularly important that the energy spectrum of the output neutron beam be tailored for specific experiments. For example, the need for beam outputs having larger uncollided neutron components, that is a beam with purer spectrum, has been recognized.
It is therefore an object of the present invention to provide a means for variably controlling neutron albedo in a toroidal fusion device so as to control the tritium breeding, neutron energy distribution, and ratio of gamma flux to neutron flux in the outboard regions of a toroidal fusion device, as well as controlling the energy spectrum of output beams of such devices.